Hcl Interview Questions Part 4
Does Java provide any construct to
find out the size of an object?
Give a simplest way to find out the
time a method takes for execution without using anyrofiling tool?
What
are wrapper classes?
Why
do we need wrapper classes?
What
are checked exceptions?
What
are runtime exceptions?
What
is the difference between error and an exception??
How
to create custom exceptions?
If
I want an object of my class to be thrown as an exception object, what should I
do?
If
my class already extends from some other class what should I do if I want an
instance of my class to be thrown as an exception object?
How
does an exception permeate through the code?
What
are the different ways to handle exceptions?
What
is the basic difference between the 2 approaches to exception handling...1>
try catch block and 2> specifying the candidate exceptions in the throws
clause?
When should you use which approach?
Is
it necessary that each try block must be followed by a catch block?
If
I write return at the end of the try block, will the finally block still
execute?
If
I write System.exit (0); at the end of the try block, will the finally block
still execute?
Does Java provide any construct to
find out the size of an object?
No there is
not sizeof operator in Java. So there is not direct way to determine the size
of an object directly in Java.
[capptitudebank.blogspot.com]
Give a simplest way to find out the
time a method takes for execution without using any profiling tool?
Read the
system time just before the method is invoked and immediately after method
returns. Take the time difference, which will give you the time taken by a
method for execution.To put it in code...
long start = System.currentTimeMillis ();
method ();
long end = System.currentTimeMillis ();
System.out.println ("Time taken for execution is "
+ (end - start));
Remember that if the time taken for execution is too small,
it might show that it is taking zero milliseconds for execution. Try it on a
method which is big enough, in the sense the one which is doing considerable
amout of processing.
[capptitudebank.blogspot.com]
What are wrapper classes?
Java
provides specialized classes corresponding to each of the primitive data types.
These are called wrapper classes. They are e.g. Integer, Character, Double etc.
[capptitudebank.blogspot.com]
Why do we need wrapper classes?
It is
sometimes easier to deal with primitives as objects. Moreover most of the
collection classes store objects and not primitive data types. And also the
wrapper classes provide many utility methods also. Because of these resons we
need wrapper classes. And since we create instances of these classes we can
store them in any of the collection classes and pass them around as a
collection. Also we can pass them around as method parameters where a method
expects an object.
[capptitudebank.blogspot.com]
What are checked exceptions?
Checked
exception are those which the Java compiler forces you to catch. e.g.
IOException are checked Exceptions.
[capptitudebank.blogspot.com]
What are runtime exceptions?
Runtime
exceptions are those exceptions that are thrown at runtime because of either
wrong input data or because of wrong business logic etc. These are not checked
by the compiler at compile time.
[capptitudebank.blogspot.com]
What is the difference between error
and an exception?
An error is
an irrecoverable condition occurring at runtime. Such as OutOfMemory error.
These JVM errors and you can not repair them at runtime. While exceptions are
conditions that occur because of bad input etc. e.g. FileNotFoundException will
be thrown if the specified file does not exist. Or a NullPointerException will
take place if you try using a null reference. In most of the cases it is
possible to recover from an exception (probably by giving user a feedback for
entering proper values etc.).
[capptitudebank.blogspot.com]
How to create custom exceptions?
Your class
should extend class Exception, or some more specific type thereof.
[capptitudebank.blogspot.com]
If I want an object of my class to
be thrown as an exception object, what should I do?
The class
should extend from Exception class. Or you can extend your class from some more
precise exception type also.
[capptitudebank.blogspot.com]
If my class already extends from
some other class what should I do if I want an instance of my class to be
thrown as an exception object?
One can not
do anytihng in this scenarion. Because Java does not allow multiple inheritance
and does not provide any exception interface as well.
[capptitudebank.blogspot.com]
How does an exception permeate
through the code?
An
unhandled exception moves up the method stack in search of a matching When an
exception is thrown from a code which is wrapped in a try block followed by one
or more catch blocks, a search is made for matching catch block. If a matching
type is found then that block will be invoked. If a matching type is not found
then the exception moves up the method stack and reaches the caller method.
Same procedure is repeated if the caller method is included in a try catch
block. This process continues until a catch block handling the appropriate type
of exception is found. If it does not find such a block then finally the
program terminates.
[capptitudebank.blogspot.com]
What are the different ways to
handle exceptions?
There are
two ways to handle exceptions,
1. By wrapping the desired code in a try block followed by a
catch block to catch the exceptions. and
2. List the desired exceptions in the throws clause of the
method and let the caller of the method hadle those exceptions.
[capptitudebank.blogspot.com]
What is the basic difference between
the 2 approaches to exception handling.
1> try catch block and
2> specifying the candidate exceptions in the throws
clause?
When should you use which approach?
In the
first approach as a programmer of the method, you urself are dealing with the
exception. This is fine if you are in a best position to decide should be done
in case of an exception. Whereas if it is not the responsibility of the method
to deal with it's own exceptions, then do not use this approach. In this case
use the second approach. In the second approach we are forcing the caller of
the method to catch the exceptions, that the method is likely to throw. This is
often the approach library creators use. They list the exception in the throws
clause and we must catch them. You will find the same approach throughout the
java libraries we use.
[capptitudebank.blogspot.com]
Is it necessary that each try block
must be followed by a catch block?
It is not
necessary that each try block must be followed by a catch block. It should be
followed by either a catch block OR a finally block. And whatever exceptions
are likely to be thrown should be declared in the throws clause of the method.
[capptitudebank.blogspot.com]
If I write return at the end of the
try block, will the finally block still execute?
Yes even if
you write return as the last statement in the try block and no exception
occurs, the finally block will execute. The finally block will execute and then
the control return.
[capptitudebank.blogspot.com]
If I write System.exit (0); at the
end of the try block, will the finally block still execute?
No in this
case the finally block will not execute because when you say System.exit (0);
the control immediately goes out of the program, and thus finally never
executes.
[capptitudebank.blogspot.com]
If you enjoyed this post and wish to be informed whenever a new post is published, then make sure you subscribe to my regular Email Updates.
Subscribe Now!
0 comments: